1. Technical Field
Example embodiments generally relate to a paper feed device configured to separate and feed sheets automatically one by one, and a paper feed cassette, a manual paper feed tray, and an image forming apparatus including the paper feed device.
2. Description of the Related Art
A related-art image forming apparatus, such as a copier, a facsimile machine, a printer, or a multifunction printer having two or more of copying, printing, scanning, and facsimile functions, forms a toner image on a recording medium (e.g., a sheet) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image bearing member (e.g., a photoconductor); an optical scanning device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; the electrostatic latent image is developed with a developer (e.g., a toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
In recent years, such an image forming apparatus is required to have a function capable of handling a wider variety of sheet types, such as postcards, glossy paper, labels, very thick paper, and very thin paper. Because a relatively smaller number of sheets is generally used in a widely used image forming apparatus, there is not a big difference in paper feed property between when only a smaller number of sheets is set and when a larger number of sheets is set. Further, a manual paper feeder is often used for feeding specific sheets of paper.
However, demand for feeding a larger number of specific sheets of paper from a normal paper feed cassette have been increased in some categories of business, such as the medical and distribution industries. Examples of such specific sheets of paper include prescription medicine packets and delivery slips, and so forth.
Meanwhile, demand for more compact and less expensive image forming apparatuses continues to increase. An example of a widely used paper feed/separation device having one such sought-after compact, low-cost configuration employed in the image forming apparatus includes a friction pad system disclosed in published unexamined Japanese Patent application No. (hereinafter referred to as JP-A-) H07-330183. In the friction pad system, a paper feed unit including a paper feed roller and a paper feed pad, and a separation unit including a separation roller and a separation pad, are provided. Frequently, a single roller having a larger diameter is used to function as both the paper feed roller and the separation roller.
One important factor that determines the ability of the friction pad system to consistently separate individual sheets of paper properly is an entry angle of a sheet into the separation unit.
FIG. 1 is a schematic view illustrating a widely used related-art paper feed/separation device. Referring to FIG. 1, it can be seen that the paper feed/separation device includes a paper feed roller 101 provided on an upstream side relative to a paper feed direction Ph of a sheet P, and a paper feed pad 103 pressed against the paper feed roller 101 by a spring 102. The paper feed/separation device further includes a separation roller 104 provided on a downstream side from the paper feed roller 101 relative to the paper feed direction Ph, and a separation pad 106 pressed against the separation roller 104 by a spring 105.
A smaller number of the sheets P conveyed from a nip N1 between the paper feed roller 101 and the paper feed pad 103 is partially separated from one another by receiving a load, that is, a separation force, from the separation pad 106 when a leading edge thereof reaches the separation roller 104 before reaching a nip N2 between the separation roller 104 and the separation pad 106. Thereafter, the sheets P are completely separated from one another by a frictional force from the separation pad 106 at the nip N2, and conveyed automatically one by one to a conveyance path provided on a downstream side from the separation pad 106 relative to the paper feed direction Ph.
The separation force decreases when an entry angle θ of the sheet P, which is an angle formed between the paper feed pad 103 and the separation pad 106, becomes larger, and vice versa. Therefore, when the separation force is improperly set for the type of the sheets P to be processed, problems may occur. For example, when the entry angle θ is too large, i.e., the separation force is too small, the sheets P are conveyed to the nip N2 without being separated from one another at all. Consequently, the sheets P are not reliably separated from one another at the nip N2, possibly resulting in double feeding and paper jams. By contrast, when the entry angle θ is too small, i.e., the separation force is too large, all of the sheets P, for example, thick paper, may get stuck at the separation pad 106 before reaching the nip N2, possibly resulting in empty feeding.
To solve such problems, ideally, it is desirable to change the entry angle θ according to the type of the sheets P.
In the paper feed/separation device according to JP-A-H07-330183, an angle formed between the separation pad and a surface of a paper loading stand is set as the entry angle of the sheet into the separation unit, and the entry angle is adjustable. However, because the entry angle may be adjusted by changing an angle of the separation pad, a condition of conveyance of the sheet from an exit of the separation pad to the conveyance path provided on a downstream side from the separation pad is changed depending on how the angle of the separation pad is changed. Consequently, thin paper may be folded or thick paper may be unsuccessfully fed after passing through the exit of the separation pad.
A paper feed device disclosed in JP-A-2000-118764 includes the same configuration as that of the paper feed/separation device disclosed in JP-A-H07-330183.
In a paper feed device disclosed in a published unexamined Japanese utility model application No. H05-22425, an angle of a sheet supporting stand is adjustable so that settings for separating the sheets from one another may be selected according to the sheet type by controlling the effect of gravity on the sheets set on the sheet supporting stand. However, when the sheet supporting stand is set almost vertically, the sheets may flop over due to gravity, possibly causing diagonal feeding of the sheets.
A manual paper feed device disclosed in JP-A-2002-002988 includes a friction adjustment mechanism configured to change a frictional force exerted by a frictional separation pad. The frictional separation pad conveys sheets by sandwiching the sheet with a paper feed roller using the frictional force. Accordingly, sheets having a certain friction therebetween may be properly fed.
However, in the above-described device, sheets such as press-fitted sheets and glossy sheets, of which surfaces adhere to one another, may not be easily separated from one another by the friction adjustable mechanism described above. In order to reliably separate such sheets from one another, it is desirable to increase an entry angle of the sheets into a nip in a separation unit so that a separation force for separating the leading edge of the sheets from one another is increased.
As described above, in the paper feed/separation devices of the related art, the angle or position of the separation pad, the paper feed pad, or the sheet supporting stand is changed so as to properly separate the sheets from one another for each sheet type. However, it is difficult to change such an angle or a position once the paper feed/separation device is installed in the image forming apparatus as a finished product.